Malnutrition and infectious diseases act synergistically to produce excessive morbidity and mortality. This study is designed to investigate the role of altered leukocyte function in enhanced susceptibility to infection in an animal model of Kwashiorkor. Rats will be fed protein deficient diets and studied sequentially until Kwashiorkor develops. Chemotaxis will be studied in vivo (modified Rebuck window) and in vitro (Boyden chamber), and opsonization will be investigated morphologically, by bacteriological techniques and through use of radioactively labeled particles. Metabolic events accompanying phagocytosis will be studied including oxygen consumption, hexose monophosphate shunt activity, and hydrogen peroxide generation. Intracellular enzymes mediating these phenomena will be measured. Cytoplasmic granules will be evaluated by morphological and cytochemical techniques. Intracellular killing of various bacteria, including Staph. aureus, E. coli, S. flexneri, S. typhimurium and Pseudomonas will be determined. Finally, membrane receptors for IgG and complement will be studied by morphological methods and with Cr51 labeled-coated erythrocytes.